The primary objective of a perforating gun is to provide effective flow paths between a wellbore and a productive reservoir. In order to achieve this, the perforating gun establishes a network of perforations through the casing and cement sheath and into the formation. Currently, all shaped charges are carried out by a perforating gun. The gun, composed from the shaped charges, the charge carrier, the detonator, and the detonation cord, is run into the hole and all charges are fired at once. The perforated zone is fractured and then isolated so that the process can be repeated for one or more zones or portions of a single zone that are uphole. Thus, the gun density and phase are crucial for successful perforations. Other factors that are important are the high impact pressure (around 10 to 15 million psi) and the tip jet speed (around 25,000 to 30,000 ft./sec). This high pressure overcomes the steel casing and formation strength and forces the solid material radially away from the jet. Several research studies published in literature show that the clearance (the distance between the shaped charge and the casing) is also important: the smaller the clearance, the higher the penetration. As the gun is usually deployed by wireline, for instance, depending on the well inclination, the gun could sit on the casing in the gravitational direction. This will produce penetrations of different lengths (i.e., higher penetrations “below” and lower penetrations “above”) that may impact production. It is worth noting that the charge carrier is a heavy well pipe that retains most of the debris after detonation.
Instead of this design, the preferred embodiment of the present invention proposes using a liner that could be centralized with packers along the completion. Knowing the precise location of the desired perforations, the liner could be designed with systems of ball-actuated sliding sleeves and shaped charges. The balls would have different sizes, as they are already used. Once a ball opens a sleeve, the corresponding shaped charge can be detonated either mechanically or electrically. Because of the packers, the charge clearance would be constant along the completion guaranteeing perforations of the same length. The sleeves could remain open after detonating the charges such that a permanent flow path would be established between the wellbore and the formation. The liner with sleeves and the shaped charge remnants could be left into the hole and recovered before another intervention or when the packers would need replacing or removing. This new method could have several main advantages over the current methods. First, it could enable a better perforating distribution both radially and axially, for an optimized production. This could also be done cheaper and faster.
In a more general description of the invention a re-fracturing method is envisioned where a liner can be placed that has shaped charges at spaced intervals so that when fixated with external packers or anchors allows perforating in locations offset from previous perforations. The fixation of the liner also acts to centralize the liner and place the shaped charges optimally near the surrounding cemented casing for optimal formation penetration. The envisioned firing order can be bottom up with progressively larger balls landing on seats or in the reverse order or a random order as needed. The fracturing of the newly created perforations enables additional production from surrounding formations, or injection for enhanced recovery through other adjacent wells. Production can take place with the liner in position or the external packers and/or anchors can be released for removal of the liner. If needed any remaining fragments of the shaped charges can be milled out or otherwise removed such as by disintegration or by dissolving, for example. Controlled electrolytic materials (CEM) can be used for the ball seat and the balls to facilitate disintegration. The same can be done with the balls landed on the seats or the seats themselves to promote flow during subsequent operations. Alternatively, a coiled tubing assembly with an internal wireline can be run with a bottom hole assembly having a resettable packer and a device to latch onto sleeves and move them mechanically or electrically with the capability of moving other sleeves to sequentially fire charges and fracture against the packer in any desired order but preferably bottom up. As used in describing and claiming the present invention, “wireline” means “wire” or “wire” akin to the TeleCoil® wire offered by Baker Hughes Incorporated of Houston, Tex., USA or a wire/cable that has the dual capability to transfer electrical power from the surface to the BHA and real-time data signals from the BHA to the surface.
Generally relevant to the field of the invention are U.S. Pat. Nos. 8,887,803 B2; 8,783,350 B2; 8,757,265 B1; 7,575,062 B2; 6,173,783 B1; 5,598,891 A; 4,974,675 A; 4,709,760 A; US 20140352968A1; US 20130292123A1; US 20130168099A1 and US 20110155377A1.
Those skilled in the art will have a greater understanding of some aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawings while understanding that the full scope of the invention is to be determined from the appended claims.